Outline

Objective

The objective was to examine the consequences of monosegmental osteotomy on overall sagittal balance of spine and pelvis according to the osteotomy level.

Methods

From 1980 to 1999, 68 patients underwent wedge osteotomy for global kyphosis related to ankylosing spondylitis (n=37) or failed back surgery with flatback and major pelvic retroversion (n=31) ( Minimum follow-up three years ). Opening wedge osteotomy was performed in the first 19 patients and closing wedge osteotomy in the remaining 49 patients. Sacral tilt (normal, 41Â°), T9 sagittal tilt (normal 11Â°), and T9 tilt (normal -11Â°) were measured on radiographs. The osteotomy was above L2 L3 disc in 26 patients and below in 42 patients.

Results

Overall, mean local correction was 44Â° and T9 sagittal tilt correction 30.6Â°. In the below L2 L3 group, mean local correction was 49Â° and T9 sagittal tilt change was +28Â° (from-2Â° to +26Â°); T9 tilt changed from -21Â° to -3Â° and ST from 6Â° to 18Â°. In the above L2 L3 group, mean local correction was 36.6Â°, T9 sagittal tilt changed from -12Â° to + 23Â° (gain, 35Â°), T9 tilt changed from -24Â° to 4Â°, and ST changed from 4Â° to 7Â°. In seven patients, functional kyphosis developed because of hip extension limitation precluding adaptation to the correction.

Conclusions

Overcorrection of posterior trunk tilt at T9 can be tolerated in patients with a good range of hip extension. Correction of pelvic retroversion (moving the sacrum to a more horizontal position) is more important in osteotomies below L3.